1. Field of the Invention
The present invention relates to a projector apparatus for projecting and displaying an image on a screen or the like by irradiating light from a light source accommodated in a housing to a transmission type liquid crystal panel.
2. Description of Related Art
A projector apparatus uses three transmission type liquid crystal panels for controlling colors, e.g., red, green and blue, synthesizes these three color components, and magnifies and projects the synthesized light through a lens. FIG. 2 is a schematic diagram showing an optical system of a general projector apparatus. From illumination light L emitted from a light source 1, red light R is separated and reflected by a dichroic mirror 2a. The separated and reflected red light R is reflected by a reflecting mirror 3a and reaches a transmission type liquid crystal panel 4a for red color.
As for green light G and blue light B transmitted through the dichroic mirror 2a, green light G is separated and reflected by a dichroic mirror 2b. The separated and reflected green light G reaches a transmission type liquid crystal panel 4b for green color. On the other hand, the blue light B transmitted through the dichroic mirror 2b is reflected by a reflecting mirror 3b, passed through a lens 5, is reflected by a reflecting mirror 3c, and reaches a transmission type liquid crystal panel 4c for blue color.
The red light R, green light G and blue light B are optically modulated when they transmit through the transmission type liquid crystal panels 4a, 4b and 4c, respectively, which panels are driven by a drive circuit in response to red, green and blue video signals, respectively. Thereafter, colors of respective optically modulated light are color-synthesized by a complex prism 6, and color-synthesized light is magnified and projected on a screen 17 by a magnifying/projecting lens (not shown). In this manner, an image can be displayed on the screen 17. In the projector apparatus, an optical axis of the light source 1 and an optical axis of an optical system are made coincident, by forming a positioning hole in one of a case accommodating the light source and a case accommodating the optical system, such as the dichroic mirror 2a, placed behind the former case, and forming a positioning pin on the other.
The light source used here is a high-pressure discharge lamp, such as a metal halide lamp and a super high-pressure mercury lamp, to which a relatively high-pressure discharge gas is sealed. This high-pressure discharge lamp (hereinafter simply called a “lamp”) is, for example, a lamp 100 having an appearance such as shown in FIG. 8, and a glass bulb 101 with a swelled portion 101a is mounted upright at the center of a concave mirror 105. The swelled portion 101a of the glass bulb 101 in which gas is sealed becomes a light emission region. One end of the glass bulb 101 is electrically connected to a male screw 104 via a metal member 103, and the other end at the top of the glass bulb 101 is connected to an electrode terminal 102 on a mirror outer surface 106 of the lamp 100 via a hole formed through the concave mirror 105, to thereby supply a discharge voltage. A flat glass 107 is mounted in front of the lamp 100.
The glass 107 has ventilation holes 100a and 100b of semicircular openings formed inside the glass 107 and at upper and lower positions of the concave mirror 105. The ventilation holes 100a and 100b form a ventilating duct for air-cooling the light emission region, the ventilating duct extending vertically in the lamp 100. The ventilation holes 100a and 100b forcibly air-cool the glass bulb 101 and its nearby area, the glass bulb 101 is driven at a startup discharge voltage of 250 kV and at a high voltage of several kV even at a discharge voltage during a stable operation, and has a high temperature. Glass of the glass bulb 101 containing sealed discharge gas is deteriorated with a long term usage, and the glass bulb 101 itself may be broken due to its lifetime or the like. The glass 107 on the lamp front side is provided also for protection from scattered matters when the glass bulb 101 happens to be broken.
However, when the glass bulb is broken, pieces of broken glass or the like stray and spread widely into the optical unit via the ventilation holes of the lamp in some cases to deteriorate the optical performance. To address this drawback, various studies have been made. For example, Japanese Patent Application Publication No. 2001-183746 (page 2, FIGS. 6 and 7) discloses a technique by which the optical performance is prevented from being deteriorated by pieces of broken glass and the like scattered from a cooling-air inlet port to the inside of an outer housing of a projector apparatus. Japanese Patent Application Publication No. 2001-183746 discloses a lamp box accommodating a light source and removably mounted in the outer housing, which lamp box is provided with: a transparent protective member disposed at a light output port of a light source; a cooling-air inlet port for guiding cooling-air from cooling means to the light source; and automatic shutter means mounted at the cooling-air inlet port for automatically opening the cooling-air inlet port by mounting the lamp box in the outer housing and automatically closing the-cooling-air inlet port by dismounting the lamp box from the outer housing.